LLVM Error with "+soft-float": "Do not know how to split the result of this operator"

[phip1611]

I can't compile the fontdue-crate because it fails with: LLVM ERROR: Do not know how to split this operator's operand!

I compile it with: cargo rustc -- -C target-feature=+soft-float,-sse,-sse2,-x87 --emit=llvm-ir

This happens with different compiler versions, independent of stable or nightly versions. I tested to build the dependencies of fontdue without problems, therefore I think Rustc/LLVM runs into a bug because of the code from fontdue.

LLVM IR

The two LLVM IR files I found after the build can be found on Google Drive.

[hkratz]

@phip1611 Quick question: Why do you use +soft-float with +x87? What do you expect floating-point code to be compiled to?

[phip1611]

Sorry, typo I made here on GitHub. It's -x87 @hkratz

[phip1611]

Update See below

In the meantime, I found out that the problem originates in hashbrown-dependency and not fontdue.

Not when building the library but when building an executable, that uses it. Minimal example:

fn main() {
    let _book_reviews = hashbrown::HashMap::<(), ()>::new();
}

Compiled with $ cargo rustc --bin bug -- -C target-feature=+soft-float,-sse,-sse2,-x87

To be exact, I'm using fontdue [-> hashbrown] in a no_std executable, that gets built with the build-std-feature of cargo. The compiler target there uses the specified CPU features from above, which should get applied to the crate itself, all dependencies, and the core library. The example above is just my minimal reproducible example.

Update
Together with the maintainer of hashbrown I figured out that the usage of RUSTFLAGS="-C target-feature=... in fact solves the problem for hashbrown because this way also dependencies are built with the requested flags. But it still doesn't solve the build problem for fontdue.

In my build setup where I originally found the issue I don't use RUSTFLAGS but a custom compiler target json file. I created a minimal reproducible example similar to my setup: https://github.com/phip1611/rust-llvm-bug-20220112-minimal-example

Update 2
When I disable the simd-feature of the latest fontdue version (which is on GitHub, not on crates.io yet!) and use that as dependency, I'm running into this error: #62729 The workaround proposed there is working.